1. Field of the Invention
The present invention relates to an image forming apparatus which is arranged to form a developed color image on an image receiving sheet coated with a developing material, and uses a photoreceptive sheet coated with microcapsules in which colorless dyes and photo-hardening agents such as photo-polymerization monomers are sealed. The image is formed through an image-making and exposing process, and a pressing process.
2. Description of the Prior Art
Japanese Patent Laid-open Publication, Tokkaisho No. 58-88739 (88739/1983), discloses one example of an image forming method. The disclosed method is such that a selective hardened image is formed through an image-making and exposing process onto a photoreceptive sheet coated with microcapsules in which colorless dyes and photo-hardening agents are sealed. The photoreceptive sheet is overlapped with an image receiving sheet coated with a developing material to be pressed, thereby to form a developed color image on the image receiving sheet. More specifically, when an image of an original is exposed onto the photoreceptive sheet (that is, subjected to an image-making exposure), photo-hardening agents on the photoreceptive sheet incident upon by the light are hardened, that is, microcapsules incident upon by the light are hardened. Accordingly, a a selective hardened image as a whole is formed. Thereafter, when an image receiving sheet coated with a developing material is overlapped onto the photoreceptive sheet to be pressed, the microcapsules which have not been hardened are broken, resulting in an outflow of the colorless dyes from the microcapsules. Subsequently, the colorless dyes flown outside the microcapsules and the developing material on the image receiving sheet react each other, thereby forming a developed color image.
On the other hand, in another color image forming method, as disclosed in Japanese Patent Laid-open Publication Tokkaisho No. 59-30537 (30537/1984). a selective hardened image is formed through an image-making exposure onto a photoreceptive sheet coated with three kinds of microcapsules each containing photo-hardening agents and one of three color materials, namely, yellow, magenta and cyan. Then, an image receiving sheet coated with a developing material is laid onto the photoreceptive sheet to be pressed, so that a developed color image is formed on the image receiving sheet. When an image of a colored original is exposed onto the photoreceptive sheet (subjected to an image-making exposure), microcapsules are selectively hardened in accordance with the wavelength of the projected light. Then, when an image receiving sheet coated with a developing material is put onto the photoreceptive sheet and pressed, the microcapsules which have not been hardened are broken and consequently the colorless dyes in the microcapsules which become cyan, magenta or yellow flow out of the microcapsules. As a result, the colorless dyes and the developing material on the image receiving sheet react each other, thereby to form a colored image.
In the above-described conventional methods, since the optimum speed in the image-making exposure process does not always agree with the optimum speed in the pressing and transferring process of a pair of pressing rollers, such drawbacks cannot be solved without having the white portions becoming fogged, or the developed color image becoming too dark if the image-making exposure speed is arranged to be the same speed in the pressing and transferring process.
In general, a good image can be formed by arranging the optimum pressing and transferring speed faster than the optimum image-making exposure speed.